1. Technical Field
The present invention relates to fabrication methods for microlens array substrates.
2. Related Art
Various types of electronic elements, including various types of wires such as data lines, scanning lines, and capacitance lines as well as thin-film transistors (“TFTs” hereinafter) are built into image display regions of electro-optical apparatuses such as liquid-crystal apparatuses. Accordingly, of the total amount of parallel light incident upon such an electro-optical apparatus, it is only possible to utilize an amount of light allowed by the numerical aperture of the pixels, unless some kind of measures are taken.
As one such measure, a microlens array containing microlenses corresponding to respective pixels has in the past been embedded into an opposing substrate, a microlens array substrate has been affixed to an opposing substrate, and so on. Doing so takes light that originally travels toward non-aperture regions outside the aperture regions of the respective pixels and focuses the light on a pixel-by-pixel basis so as to conduct the light to the aperture regions of the pixels. The electro-optical apparatus can produce a bright display as a result.
A high lens efficiency is a basic requirement in such microlenses. As such, methods for fabricating microlenses having aspheric surfaces have been proposed.
For example, JP-A-2004-70283 discloses a method for fabricating a microlens that includes forming on a substrate a first film that has an etching rate higher than the substrate, forming on the first film a mask in which a hole is provided at a position corresponding to a center of the microlens to be formed, and forming in the substrate an aspheric recess that defines a curved surface of the microlens by wet-etching the first film over the mask.
According to JP-A-2004-70283, after being formed on the substrate, the first film is subjected to annealing at a predetermined temperature so as to bake the first film and control the etching rate thereof. However, the inventors of this invention discovered that the annealing in this method causes the substrate to warp, causing problems in the subsequent steps of forming films and the like. A large warp in the substrate makes it difficult to position the element substrate and the opposing substrate when affixing the substrates to each other, making it generally difficult to affix the element substrate and the opposing substrate to each other. A large warp in the substrate can also make it impossible to carry out vacuum suction during the substrate transportation, resulting in errors, and can furthermore result in localized forces being applied when polishing the substrate surface during a smoothing process, which can cause the film to peel off.